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Old 12-04-2012, 11:52 AM   #16
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re-routing wires


Quote:
Originally Posted by Rochsolid View Post
I agree with electures on this. I usually run 2 cables per 3/4" hole. That's the norm where I'm from, inspectors will fail it if we don't. Also a 1 1/4" hole in your 2x10 joist is a very big hole, I would be worried about the structural strength now of those joists
As a general rule, you can make large holes within the middle 1/3rd of a joist. It's notching or making holes in the top or bottom 1/3 that rapidly destroy the load bearing capacity of a joist.

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Old 12-04-2012, 05:55 PM   #17
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re-routing wires


FRom the 2011 NEC;

334.80 Ampacity.
The ampacity of Types NM, NMC, and
NMS cable shall be determined in accordance with 310.15.
The allowable ampacity shall not exceed that of a 60C
(140F) rated conductor. The 90C (194F) rating shall be
permitted to be used for ampacity adjustment and correction
calculations, provided the final derated ampacity does not exceed
that of a 60C (140F) rated conductor. The ampacity of
Types NM, NMC, and NMS cable installed in cable tray shall
be determined in accordance with 392.80(A).
Where more than two NM cables containing two or
more current-carrying conductors are installed, without
maintaining spacing between the cables, through the same
opening in wood framing that is to be sealed with thermal
insulation, caulk, or sealing foam, the allowable ampacity
of each conductor shall be adjusted in accordance with
Table 310.15(B)(3)(a) and the provisions of 310.15(A)(2),
Exception, shall not apply.
Where more than two NM cables containing two or
more current-carrying conductors are installed in contact
with thermal insulation without maintaining spacing between
cables, the allowable ampacity of each conductor

shall be adjusted in accordance with Table 310.15(B)(3)(a).

As long as the holes are not sealed, or the cable is not in contact with thermal insulation, no derating is required.

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